Open AccessResearch Comparison of fertility results after vaginal insemination using different thawing procedures and packages for frozen ram semen Address: 1 Team Semin, Norwegian Scho
Trang 1Open Access
Research
Comparison of fertility results after vaginal insemination using
different thawing procedures and packages for frozen ram semen
Address: 1 Team Semin, Norwegian School of Veterinary Science, PO Box 8146 Dep., N-0033 Oslo, Norway, 2 Department of Production Animal Clinical Sciences, Norwegian School of Veterinary Science, PO Box 8146 Dep., N-0033 Oslo, Norway, 3 Department of Animal and Aquacultural Sciences, Norwegian University of Life Sciences, PO Box 5003, N-1432 Ås, Norway and 4 Department of Clinical Sciences, Division of
Reproduction, Faculty of Veterinary Medicine and Animal Science, Swedish University of Agricultural Sciences, PO Box 7054 Ultuna, SE-75007 Uppsala, Sweden
Email: Heiko Paulenz - heiko.paulenz@veths.no; Tormod Ådnøy - tormod.adnoy@umb.no; Lennart Söderquist* - lennart.soderquist@kv.slu.se
* Corresponding author
Abstract
Background: The effect of different thawing procedures for ram semen frozen in minitubes and
mini straws on the fertility of sheep was tested in a field trial
Methods: Altogether, 719 Norwegian Crossbred ewes, aged between six months and
six-and-a-half years from 8 farms, were inseminated vaginally in natural oestrus with frozen-thawed semen
Minitubes were thawed at 70°C for 8 sec (T70) and mini straws either at 50°C for 9 sec (S50) or
at 35°C for 12 sec (S35)
Results: Vaginal insemination with 200 × 106 spermatozoa resulted in 25-days non-return rates of
63.2, 59.6, and 62.5% (overall 61.8%), respectively, and lambing rates of 56.8, 55.0, and 59.2%
(overall 57.0%), respectively No significant effect on fertility (as 25-days non-return- or lambing
rate) was seen for straw type/thawing temperature (P = 0.5/0.5), but semen filled in mini straws
and thawed at 35°C resulted numerically in the highest lambing rate (59.2%) A significant effect
was, however, seen for farmer (P = >0.0001/>0.0001) and ram (P = 0.009/0.002) Moreover, age
of the ewes had a significant effect on the NR rate (0.007), but not on lambing rate (P = 0.2)
spermatozoa, filled in mini straws and thawed at 35°C is a simplified technique that under field
conditions and used on a do-it-yourself regime gives acceptable lambing rates in Norway
Background
The fertility of Norwegian Crossbred ewes is very high,
with natural mating being predominant Because the
aver-age flock size is only approximately 52 adult animals, a
cooperative scheme for breeding has been developed
During the mating season rams are moved between farms
that belong to the same "ram circle" or breeding group,
according to their breeding requirements [1,2]
In the 1960s cervical insemination with frozen-thawed ram semen was developed in Norway [3] for routine use
in artificial insemination (AI) At that time AI was intro-duced as a supplement to natural mating and therefore only less than one per cent of the ewes were inseminated artificially over the next three decades The routine cryop-reservation protocol developed during this period included manually filling/sealing and freezing in
Published: 28 September 2007
Acta Veterinaria Scandinavica 2007, 49:26 doi:10.1186/1751-0147-49-26
Received: 12 June 2007 Accepted: 28 September 2007 This article is available from: http://www.actavetscand.com/content/49/1/26
© 2007 Paulenz et al; licensee BioMed Central Ltd
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Trang 2minitubes (0.25 ml, Minitüb GMBH, Tiefenbach,
Ger-many), and subsequent thawing at 70°C (±2°C) for 8 sec
The recommendation that thawing of ram semen should
be fast (few seconds) and consequently at a relatively high
temperature (70°C) was based upon the results obtained
by Aamdal and Andersen [4,5] They found a considerably
better semen quality, measured as sperm motility and
sperm membrane integrity, after thawing of semen in 0.25
ml PVC straws, which were similar in shape and thickness
to minitubes, at 70°C for 8 sec compared with 35°C for
15 or 30 sec using straws It is noteworthy that semen at
that time was frozen at lower concentrations (500 × 106/
ml) compared to the routines used in the last three
dec-ades (1000 × 106/ml) This difference might have
implica-tions on semen quality after freezing and thawing
In the middle of the 1990s the Norwegian animal health
authorities issued several restrictions on the movement of
sheep between flocks, in order to control the emergence of
scrapie and maedi These restrictions are still prevailing
and, therefore, moving rams between farms is currently
prohibited in many regions, reducing the effectiveness of
the ram circles As a consequence, the use of AI increased
to about 3.5 per cent during the last decade [6-11],
emphasizing the need to use more automatic systems for
semen processing at the AI-stations Therefore, in 2001 a
field trial based on do-it-yourself (DIY) inseminations
[12] was conducted with the aim to compare fertility
results after cervical AI with minitubes, thawed at 70°C
for 8 sec, and conventional mini straws (0.25 ml, IMV,
L'Aigle, France), thawed either at 70°C for 5 sec, 50°C for
9 sec or 35°C for 12 sec The results showed that cervical
AI using minitubes resulted in the highest overall lambing
rates and was superior to mini straws (approximately 5 to
10% units) independent of thawing procedure used The
lowest lambing rates, however, were achieved using mini
straws thawed at 70°C for 5 sec Many of the farmers
par-ticipating in that field trial complained that the
combina-tion of short thawing time and high temperature made it
difficult to handle the thawing of the thin mini straws in
a proper way The use of mini straws, however, would
allow automatic filling and sealing of ram semen at
AI-sta-tions as well as more efficient storage in liquid nitrogen
containers Therefore, the superior fertility results were
evaluated carefully in relation to the possible application
of a more rational semen production and simplified
semen handling at AI when using mini straws thawed at
35°C Consequently, from 2002 freezing of ram semen in
mini straws and subsequent thawing at 35°C was
consid-ered as the method of choice in Norway
Successful application of AI in sheep also depends upon
the availability of a cheap and effective insemination
tech-nique To attain this goal, an AI technique had to be
estab-lished that easily could be applied under field conditions
by the farmers themselves Vaginal insemination [13] is easy to perform because only an insemination pipette is required A Norwegian field trial based on DIY insemina-tions and performed in 2002 [14] compared vaginal and cervical deposition of frozen-thawed semen, and found somewhat higher fertility results (circa 5% units) for cer-vical deposition compared to vaginal with a significant difference in the overall lambing rate However, the study also revealed significant effects both of the farmers per-forming the inseminations as well as of an interaction between farmer and deposition site Four out of ten farm-ers had numerically better results after vaginal compared
to cervical deposition, while five farmers had the opposite results Based on these results, vaginal insemination, being a simple, less costly and less time consuming tech-nique, was recommended for routine use for AI of ewes with frozen-thawed semen in Norway starting in 2003
Despite the above described, recommended change of semen package and deposition site applied in Norway, the influence on fertility of different straw types and thawing temperatures using vaginal insemination remains to be established
Therefore, the aim of the present study was to compare, under field conditions, the fertility results after vaginal insemination of ewes using semen frozen in mini tubes and thawed at 70°C for 8 sec with semen frozen in mini straws and thawed at 50°C for 9 sec or at 35°C for 12 sec
Methods
Rams and semen processing
Semen from 7 mature Norwegian Crossbred rams with known fertility was used for AI The animals were owned
by the Norwegian Association of Sheep and Goat Breeders (NSG) and housed at the NSG Semin AI station in south-eastern Norway, near Hamar, a region with inland cli-mate
Semen was collected three to four times weekly per ram during the breeding season (November–December, Northern Hemisphere) using an artificial vagina Each ejaculate was collected in a pre-warmed graduated glass vial Semen quality was assessed, and to be accepted as a donor, every ram had to fulfil the following demands con-cerning semen quality: volume ≥ 0.5 ml, macroscopic good visual mass activity, sperm concentration ≥ 3 × 109/
ml, progressive sperm motility ≥ 75%, and normal sperm morphology ≥ 90% Motility was assessed subjectively and membrane integrity as well as morphology evaluated after eosin-nigrosin staining During the whole produc-tion period volume, mass activity, sperm concentraproduc-tion and motility were evaluated routinely, while sperm mor-phology was only assessed occasionally Sperm concentra-tion was estimated with a spectrophotometer (Accucel,
Trang 3IMV, L'Aigle France), which was calibrated for ram semen.
Using a phase contrast microscope sperm motility was
assessed at 200 × magnification and morphology at 400 ×
magnification
The ejaculates were placed in a water bath (35°C)
imme-diately after collection, and semen quality was assessed
Within 10 minutes after collection each ejaculate was
diluted 1+4 to 1+6 with a 35°C warm milk-based
extender (E 1), prepared from non-fatty milk powder
(11% w/v) and distilled water, heated to 95°C for 10 min,
and then cooled to room temperature before egg yolk
(5%; w/v), penicillin and streptomycin was added Each
glass with the extended semen was wrapped with tissue
paper to protect against cold shock The semen was then
cooled to 5°C during approximately 30 minutes by
plac-ing it in a room at that temperature The cooled semen
was then diluted 1+1 with an extender (E 2) of equal
tem-perature Extender 2 was the same as E 1, but with the
addition of glycerol (14%; v/v) resulting in a final glycerol
concentration of 7% Addition of E 2 was performed
step-wise during a couple of minutes After this second
dilu-tion the semen was kept at 5°C to allow glycerol
equilibration and adaptation to this temperature for 90 to
120 minutes Then the semen was re-concentrated by
cen-trifugation (1000 g/10 minutes) removing enough
super-natant to yield a calculated final sperm concentration of
about 1000 × 106/ml From the cooled and
re-concen-trated semen one-third part was used to manually fill
aliq-uots of 0.2 ml into minitubes (0.25 ml, Minitüb,
Tiefenbach, Germany), and the remaining part was used
for automatic filling (MRS 3, IMV, L'Aigle, France) of mini
straws (0.25 ml, IMV, L'Aigle, France) resulting in an
insemination dose of 200 × 106 spermatozoa The
minitubes were sealed with plastic balls, while the open
end of the mini straws were welded automatically using
ultra sound Freezing was performed in a programmable
freezer (Digicool 5300, IMV, L'Aigle France) where the
temperature decreased to -10°C at a rate of 5°C/min and
from -10°C to -130°C at 60°C/min Thereafter the straws
were transferred to liquid nitrogen From each batch and
each ram one straw was thawed, and only batches
show-ing at least 50% progressive motility were approved for
use
Ewes and artificial insemination
During a period of about five weeks, from the middle of
November to the middle of December 2004, a total of 719
Norwegian Crossbred ewes were inseminated artificially
The ewes were between six months and six-and-a-half
years old at the time of insemination and housed at 8
dif-ferent farms that were located in the mid part of Norway,
in a region (Trøndelag) with mostly coastal climate All
farms received semen doses from all rams The number of
semen doses produced from each ram, however, was not
identical In average 103.7 AI-doses, with a range from 31
to 179, were used from each ram In general, the farmers checked oestrus twice daily with a time interval of about
12 hours using a teaser ram fitted with an apron The ewes were inseminated once and AI was recommended between 12 – 24 hours after detection of standing oestrus
The farmers involved in the study had all performed inseminations themselves in their flocks during several years, and were, thus, considered as experienced insemi-nators In the farms selected for this trial all ewes were inseminated The ewes were inseminated vaginally with a dose of approximately 200 × 106 frozen-thawed spermato-zoa The vaginal inseminations were made with an insem-ination pipette with a diameter of 5 mm and a rounded tip (Minitüb GmbH, Tiefenbach, Germany); without using a speculum, the lips of the vulva were parted and the semen was placed as deeply as possible into the vagina, as described by Fairnie and Wales (1982)
Thawing procedures
Minitubes were thawed in water in thermos flasks at 70°C for 8 seconds (T70) Mini straws were thawed either at 50°C for 9 sec (S50) or at 35°C for 12 sec (S35) The thawing time was measured with a timer
Experimental design
The females were allocated to three parallel groups within each flock based on the two straw types and different thawing temperatures (see thawing procedures and abbre-viations above) The ewes were consecutively inseminated when showing natural oestrus as follows: T70, S50, and S35, respectively, and then starting again from the begin-ning with a new round For each round semen from a new ram was used
Fertility assessments
To detect ewes returning to oestrus, all ewes were checked from day 12 to day 25 after insemination using a teaser ram Ewes not returning to oestrus were considered preg-nant, and recorded as the percentage of ewes that did not return to oestrus at 25 days after AI (25-days NR) Lamb-ing rates (percentage of ewes lambLamb-ing) were recorded for each farm during the following spring Moreover, the farmers recorded ewes returning to oestrus later than 25 days after insemination as well as abortions All record-ings were made by the farmers and a written report was forwarded from each farmer
Statistical analysis
The binomial response NR rate (not returned to oestrus) and lambing rate were analyzed using a linear logistic model: the genmod procedure for categorical data (Statis-tical Analysis Systems statis(Statis-tical package, version 6.12; SAS Institute Inc., Cary, NC, USA)
Trang 4The model chosen was:
log odds of NR and lambing rate
= age of the ewe + farmer + ram + straw type/thawing
tem-perature
where NR and lambing rate for a ewe is either yes or no,
age of ewe at parturition time is: 1, 2, 3, 4 or >4 years,
farmer is one of 8 farmers,
ram is one of 7 different rams used, and
straw type/thawing temperature is either T70, S50 or S35
The parameters were fitted by the maximum likelihood
principle, and effects tested by Chi-Square [15,16]
Signif-icances of main effects (not accounting for other effects)
were confirmed by Fisher's exact tests
Several alternative statistical models were tried, including
combinations of main effects with interactions The
results of the chosen model were in accordance with other
simpler models, and the ones with interactions that were
possible to run Because of the fact that the farmers both
were responsible for the effects of the flock management,
for example oestrus check, and also performed the
insem-inations, the effect of the inseminator could not be
included in addition to farmer To avoid overlapping only
the effect of farmer was included in the statistical model
The level of significance was set to 0.05 The contrast
between the 3 comparable pairs of thawing procedures
(T70-S50; T70-S35; S50-S35) was tested with chi-square
both for non-return and lambing rate
Results
P-values
The levels of significance for the effects of age of the ewe, farmer, ram and straw type/thawing temperature are pre-sented in Table 1 Farmer and ram had a significant influ-ence both on the NR- and lambing rates, while age of the ewes had only a significant influence on the NR-rates No significant main effects were seen for straw type/thawing temperature on fertility
Fertility
The 25-days NR- and the lambing rates for the different straw types and thawing temperatures are shown in Table
2 The average 25-days NR rate was 61.8%, ranging between 40.0 to 82.4% in the different farms, and the average lambing rate was 57.0% (range 37.0 to 82.4%) The difference between the overall 25-days NR result and the lambing rate was 4.8% units (n = 35) Out of the 35 ewes 31 returned to oestrus later than 25 days Four ewes (0.6%) aborted and all abortions were found in one farm The difference between the overall 25-day NR result and the lambing rate varied among farms (0.0–11.1%) and age of the ewes, and was higher among primipari ewes (18.3%) compared to pluripari ewes (2.3%)
Ewe, ram and farmer
On average 90 ewes, with a range from 40 to 160, were inseminated per farm The average time from detection of standing heat to insemination was approximately 18 hours with a range from 10 to 25 hours The average number of lambs per ewe was 1.5 for primipari ewes (n = 65), 1.8 for pluripari ewes (n = 345), and 1.75 over all in the study (n = 410)
The fertility results for the different rams varied between 50.0 and 74.3% (average 61.8) for the 25-days NR rate and between 42.8 and 68.2% (average 57.0) for the lamb-ing rate The difference between the 25-days NR and the lambing rate varied between 0.0 and 7.3% units for the individual rams
Table 1: P values for the effects of age of the ewe, farmer, ram and straw type/thawing temperature P values and chi-square (25-days NR- and lambing rates) for the effects of age of the ewe, farmer, ram and straw type/thawing temperature in 719 ewes, aged between six months and six-and-a-half years, inseminated vaginally with 200 × 10 6 frozen-thawed spermatozoa using different packages and thawing temperatures, collected from 7 mature rams.
Source of variation Degrees of
freedom
Straw type/thawing temperature 2 3.8 6.7 0.515 0.450
NR = 25-days non-return
Trang 5Pair wise comparison
P values and chi-square for the fertility results, when
com-paring the three different straw types/thawing
tempera-tures pair wise are shown in Table 3 No significant
differences could be seen between the fertility rates
Discussion
No significant effect on fertility, expressed as 25-days
non-return- or lambing rate, was seen in the present study for
straw type/thawing temperature A significant influence of
farmer, ram, and age of the ewes was seen on the fertility
results Semen filled in mini straws and thawed at 35°C
gave numerically the highest lambing rate with 59.2%,
while the 25-days NR rate was 62.5% The overall national
fertility results in the same season (2004), only available
as 25 days NR rates, were 61.3% (n = 14327) and in
accordance with the results obtained in this study [11,17]
In the literature, the influence of different packaging on
sperm survival has been studied, using identical thawing
procedures by Maxwell et al [18], while Söderquist et al
[19] compared thawing of ram semen frozen in mini
straws at 70, 50 and 35°C and found that the post-thaw sperm motility, as well as the percentage of spermatozoa depicting intact membranes, were significantly higher in straws thawed at 70°C compared to at 35°C No statisti-cally significant difference was, however, found for these parameters when the results from thawing at 70°C and 50°C were compared Later, in a field trial with a limited number of inseminations, Söderquist et al [20] reported that thawing of mini straws at 50°C for 9 sec, instead of 70°C for 5 sec, did not seem to further affect neither fer-tility nor fecundity
In a recent study Paulenz et al [12] thawed mini tubes at 70°C for 8 sec (T70) and mini straws either at 70°C for 5 sec (S70), 50°C for 9 sec (S50) or 35°C for 12 sec (S35)
No significant effects were seen for straw type/thawing temperature after cervical insemination with 200 × 106
spermatozoa on fertility expressed as 25-days
non-return-or lambing rate There was, however, a significantly higher lambing rate for T70 compared to S35 but not compared
to S50 The highest lambing rate was achieved for mini tubes (T70) However, in the present study the highest
Table 3: Comparison of fertility results using different packages and thawing temperatures P values and chi-squared (25-days NR- and lambing rates) for the comparison of fertility results using different packages and thawing temperatures after vaginal insemination of
719 ewes, aged between six months and six-and-a-half years, with 200 × 10 6 frozen-thawed spermatozoa collected from 7 mature rams.
Comparison between
minitubes and mini straws
Degrees of freedom NR Lambing NR Lambing
T70 = Minitubes thawed at 70°C for 8 sec
S50 = Mini straws thawed at 50°C for 9 sec
S35 = Mini straws thawed at 35°C for 12 sec
NR = 25-days non-return
Table 2: Fertility results for the different packages and thawing temperatures Non-return (25-days NR) and lambing rates for different packages and thawing temperatures after vaginal insemination of 719 ewes, aged between six months and six-and-a-half years, with
200 × 10 6 frozen-thawed spermatozoa collected from 7 mature rams.
Straw type/Thawing
temperature
Number of inseminations
Number Percentage Number Percentage
T70 = Minitubes thawed at 70°C for 8 sec
S50 = Mini straws thawed at 50°C for 9 sec
S35 = Mini straws thawed at 35°C for 12 sec
Trang 6results were seen using mini straws (S35), but no
signifi-cant difference was found when comparing T70 and S35
The discrepancy between these two studies is unclear, but
the different deposition sites may have contributed to the
result
Minitubes are similar to mini straws with the exception of
their surface-to-volume ratios, the thickness of the
mate-rial in the tube and the way the ends are sealed after filling
the straws Especially the larger surface-to-volume ratio of
the mini straws may have implications for both the
freez-ing and the thawfreez-ing rates Therefore, it would be optimal
to include also the freezing rate, when comparing
differ-ent straw types In a field trial under practical conditions,
however, only a limited number of variables could be
tested, why we in the present study chose to use the
rou-tine freezing rate for both straw types Further studies are
needed to assess the influence of different freezing rates
on different packages
The variation in fertility results between the individual
farmers in the NR rates as well as in lambing rates are in
accordance with results from our earlier studies
[12,14,20-22] These differences among the farmers represent not
only the level of technical skill of insemination itself but
also flock conditions like detection of heat and oestrus
symptoms [23] Other factors, like e.g feeding or animal
handling, might also have contributed to the differences
seen herein On the whole, the above mentioned factors
are of great importance for successful AI results
underlin-ing the need for a continuous guidance and further
train-ing of the DIY-farmers in order to optimise the conditions
on the farms
There were significant differences in the NR and lambing
rates of ewes inseminated with semen from different
rams Such variations in fertility of rams are well
docu-mented and have been reported using fresh semen by
Salamon and Robinson [24] following cervical
tion and Paulenz et al [21] following vaginal
insemina-tion For the use of frozen-thawed semen sire effects are
described by Maxwell [25], Eppleston et al [26,27], and
Eppleston and Maxwell [28] following laparoscopic
insemination, by Colas [29], Windsor [30], and
Söder-quist et al [20] following cervical insemination, and by
Paulenz et al [14] following vaginal insemination The
rams used as donors in this study were selected after an
estimation of a breeding value that was based on the
results of natural mating in the previous season Though
the breeding value includes fertility as an important
fac-tor, the variation observed between the seven rams
emphasises the need for improved methods for the
selec-tion of AI-rams
It is noteworthy that the difference between the overall 25-day NR result and the lambing rate was about twice as high in the present study as found in our earlier studies [12,14,22] This increased value was obviously caused by
a much higher difference seen among primipari ewes (18.3%) compared to pluripari ewes (2.3%) The reason for this is not fully understood, but several factors may be
of importance, e.g insufficient oestrous control in some farms, incapacity to show oestrus caused by low ranking, hidden anatomical or physiological disorders and defects
It is desirable to find a more rational procedure for semen production at the AI station, but also to introduce a sim-ple and safe thawing procedure that could be applied under practical field conditions in Nordic countries, sim-ilarly on a large scale by all farmers The use of mini straws allows automatic filling and sealing of ram semen at AI-stations as well as more efficient storage in liquid nitrogen containers Furthermore, the use of mini straws and thaw-ing them at 35°C diminishes the risk for maltreatment at
AI such as overheating the semen [19] In addition, vagi-nal deposition of frozen-thawed semen simplifies the AI technique, being simple, less costly and less time consum-ing compared to others, also brconsum-ingconsum-ing into focus the ani-mal welfare aspects at AI
Conclusions
The use of vaginal deposition of frozen ram semen con-taining approximately 200 × 106 spermatozoa, filled in mini straws and thawed at 35°C is a simplified technique that under field conditions and used on a DIY basis gives acceptable lambing rates in Norway Furthermore, freez-ing of ram semen in mini straws would also result in a more rational semen production and simplified semen handling at the AI centres
Competing interests
The author(s) declare that they have no competing inter-ests
Authors' contributions
HP was main responsible and involved in all parts of the study LS participated in all parts of the study but not in the statistical analysis TA participated in the design of the study and performed the statistical analysis All authors read and approved the final manuscript
Acknowledgements
This work received financial support from The Research Council of Nor-way and The Norwegian Association of Sheep and Goat Breeders.
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